The present invention relates to oil shale retorting processes and, more particularly, to retorting processes for the retorting of oil shale employing hot flue gases for preheating the raw oil shale.
The pyrolysis of oil shale by solid-to-solid heat transfer techniques to convert the kerogen content of oil shale into oil and other gaseous hydrocarbons is well known as exemplified by the disclosures in U.S. Pat. Nos. 3,265,608 and 3,691,056. In these prior art processes, oil shale is preheated and thereafter pyrolyzed by solid-to-solid heat transfer contact with heat-carrying bodies to produce shale oil and other effluent vapors. Upon completion of the kerogen conversion the heat-carrying bodies are recycled through a reheating zone for further use in pyrolyzing additional preheated oil shale.
In U.S. Pat. No. 3,925,190, Whitcombe, et al discloses an improvement to such processes which utilizes the residual sensible heat of the flue gases previously employed in the process to heat the heat-carrying bodies for preheating the raw oil shale prior to the pyrolysis thereof. The preheating of the crushed raw oil shale by the hot flue gases is accomplished in a series of at least two dilute phase fluidized beds, i.e. gas lift lines or lift pipes, having an incineration zone interposed therebetween through which the flue gas from the final preheat zone is passed prior to contacting and preheating additional oil shale to a temperature between that of the initial raw shale temperature and the final preheat temperature prior to introduction of the preheated shale into the pyrolysis zone. The single FIGURE sets forth in simplified form one configuration of such oil shale retorting appartus incorporating hot flue gases for the preheating of the raw oil shale.
Briefly, it can be seen that raw oil shale 10 is introduced at the bottom of a first lift pipe 12 along with hot gases 14. A dilute phase fluidized bed is thus created within the first lift pipe 12. As the raw shale 10 rises in first lift pipe 12 in the presence of the hot gases 14, it is heated. The heated raw shale 10' and hot gases 14 pass into the separator 16 of first lift pipe 12 from whence the hot gases 14 containing entrained particulate matter are passed to a final scrubber 18 and the heated raw oil shale 10' is directed to the bottom of a second lift pipe 20. In similar manner, within the second lift pipe 20 the heated shale 10' is mixed with hot gases 14' being of a hotter temperature than the hot gases 14. As can be seen, within the separator 16' of second lift pipe 20, the now hotter raw oil shale 10" is directed to the bottom of a third lift pipe 22 while the hot gases of a lower temperature after transferring a portion of the heat therein to the shale 10' are directed to the bottom of lift pipe 12 as the hot gases 14. According to the prior art, from the third lift pipe separator 16", the raw oil shale 10'" is directed into the retort 24 and the cooled hot gases 14" are passed directly into an incinerator 26 as indicated by the dashed arrow connector wherein they are heated by the burning of air 28 and fuel 30 to emerge as hot gases 14' which enter the bottom of the second lift pipe 20 as hereinbefore described.
From the retort 24, the pyrolyzed shale 32 is removed as a waste product while the vapors 34 are directed into a quench tower 36. The pyrolysis vapors 34 produced in the retorting process entrain certain amounts of very fine solids or particulate matter which are removed from the bulk of the pyrolysis vapors 34 in the quench tower 36. The clean pyrolysis vapors 38 are directed to further recovery apparatus (not shown). The solids are removed as a bottoms oil mixture 40 of condensed heavy pyrolysis oil and solids. Before this heavy bottoms oil in the mixture 40 can be combined with the remainder of the oil recovered by the process or before it is further processed, installation of a centrifuge, filter, or other solids separation device 42 is desirable so that a clean bottoms oil 44 can be produced. The separation device 42 makes a clarified oil containing a low amount of solids in the oil which is drawn off as the clean oil 44 which is processed by further recovery apparatus (also not shown). Additionally, the solids separation device 42 produces a sludge 46 composed of a concentration of solids in bottoms oil. The disposal of the sludge 46 creates a disposal problem unlike the clean flue gases 48 and solids (particulate matter) 50 which are produced from the hot gases 14 emerging from first lift pipe 12 by the final scrubber 18 connected thereto. In addition, the oils contained within sludge 46, if disposed of in conjunction with sludge 46, represent a loss of potentially usable product in the recovery process.
Wherefore, it is the object of the present invention to provide method and apparatus for eliminating the sludge as a disposal problem and for utilizing the otherwise lost oils contained therein.